New phenomenon found?

Over the past few months, I've been quietly gathering evidence on a strange radio phenomenon I've noticed in the local area.

Regular readers will know the QTH is based on an old copper mine.  This sounds fantastic - and it is - for radio.  But it's dissolved iron that is probably responsible for the world beating ground characteristics to be found here, because it is by far the most common element.

Bacteria (actually, Archaea, as separate Kingdom) eat away at iron bound with sulphur, producing sulphuric acid.  I've measured pH as low as 1 on the mountain.  At pH of below around 5 or so, iron is in the Fe2+ state, and is dissolved (handy to know if you ever have a rust stain on the bath - just put some acid toilet cleaner on it!)  At above pH 5, the iron stops being soluble, and becomes the more familiar Fe3+ in the form of a 'floc' that smothers the river bed.

Afon Goch, near Amlwch.  The pH remains low enough, even at 1km or so from source, to keep most of the iron in solution.

So as well as having a very high level of mineralisation, there is also highly acidic conditions.  Thinking about it today, I realise that sounds a bit like a battery!  I must think about that a bit more.

But the strange thing I've found is that, at a very precise and repeatable location, commercial FM radio suffers 'crosstalk' for a moment.  Now, crosstalk is not uncommon, and we are located relatively high up, in line-of-sight to many Irish Sea areas.

Acid drainage from Parys runs under the road below the white cursor (you can see vents to the surface in a line running roughly centre to upper right corner)

But this kind of crosstalk occurs only when I move in a car over an underground, highly acidic mine drainage stream - appropriately known as 'afon goch' (red river).  The interference only happens momentarily - just a second or so, exactly as the stream passes underneath me.  Afon Goch, incidentally, is the largest single source of heavy metal pollution into the Irish Sea.

It could be a coincidence, and that it's geography, rather than the river that is responsible.  That's why I've been testing it many times.  Stratified atmospheric conditions do not seem to be responsible, as it occurs under windy and calm weather alike, and regardless of season.  And it doesn't happen anywhere else!

Well, that's something to think about some more.  Perhaps the acid drainage produces some kind of earth current?  Metal detectorists know very well about the crazy effects of mineralised ground which, looking at some online data this morning, tells me is due to a modified magnetic field (which is pretty obvious, really, given it's not only metal but iron in the ground).